The present invention relates to a method of biological purification of sewage during which the purified sewage after its mechanical pre-treatment is subjected to the process of biological removal of pollution with activated sludge under aerobic and/or anoxidic and/or anaerobic conditions with following sedimentation and at that the activated sludge comes back into the purification process and its excess is carried away this process.
The invention also relates to an equipment for performing this method which includes a basket for mechanical pre-treatment with a pre-connected inlet of purified sewage, an activation space with aerating elements, a feeding tank with a feed roll, a recirculation sludge pump for pumping the activated sludge from the feeding tank bottom into the inlet zone of the activation space and the purified sewage withdrawal.
It is known that there exist a method of biological sewage purification during which the purified sewage after its mechanical pre-treatment is subjected to the process of biological removal of pollution with activated sludge under aerobic and/or anoxidic and/or anaerobic conditions with following sedimentation and at that the activated sludge comes back into the purification process and its excess is carried away this process.
The mentioned method is applied in various sewage treatment plants from small domestic sewage plants up to sewage treatment plants for higher numbers of equivalent residents.
It is known that when applying this method, i.e. during operation of these sewage treatment plants, floating impurities and the activated sludge are flooded up on the level of the feeding tank during sedimentation. This phenomenon is frequent mainly in smaller sewage treatment plants for the reason of considerable irregularity of hydraulic load. Removing of floating impurities and sludge is often solved in larger sewage treatment plants with the aid of a special equipment that wipes off or pumps these impurities from the level of the feeding tank.
In smaller sewage treatment plants where the occurence of these undesirable effects is frequent and quantities of floating impurities and sludge are considerable the equipment for removing of floating impurities and sludge is missing as a rule for economic reasons and removing of these impurities and sludge is solved manually as a rule. When removing it is necessary together with floating impurities to remove also the floating sludge which is as a rule several times more than floating impurities or it is necessary to mix off mechanically the gaseous phase from the float out activated sludge and thus to separate the float sludge from the system of sewage purification from floating impurities what considerably reduces the quantity of impurities necessary to remove form the level of the feeding tank.
This method of removing of floating impurities is considerably time demanding and during stirring the floating activated sludge and simultaneous feeding of purified sewage this activated sludge leaks into the outlet what considerably deteriorates the resulting parameters of the purified sewage.
In systems of sewage purification when for sedimentation of activated sludge the vertical feeding tank is used it is also necessary to remove manually the floating impurities from the feed roll placed in the feeding space.
Also in this feed roll the floating impurities together with the float out activated sludge are catched what also increases the quantity of matters that must be removed from the system.
The invention sets as a goal to remove or at least to considerably limit the above mentioned insufficiencies.
The substance of the biological method of sewage purification during which the purified sewage after its mechanical pre-treatment runs through the purifying process of biological removal of pollution with activated sludge under aerobic and/or anoxidic and/or anaerobic conditions with following sedimentation of the mixture of purified sewage and activated sludge for the purpose of separation and at that the activated sludge comes back into the purification process and the possible excess of the sludge is carried away the purification process and the separated water leaves the purification process, according to the invention consists in it that during the purification process the separated water in determined time intervals is pumped off from the separation process and the sedimentation of the remained part is subsequently interrupted by its intensive stirring whereupon the sedimentation process continues.
A further feature of this method is that the quantity of water pumped in determined time intervals corresponds approximately to the expected spasmodic feeding of purified sewage into the purification process during the time of pumping of sewage from the feeding space, intensive stirring, and subsequent stabilization of the purification process.
From the point of view of achieving the exceptionally good purification effect it is advantageous if after interruption of sedimentation the floating impurities are sucked off from the level of separated sewage and further on that the sucked floated impurities come back into the activating purification process.
The substance of the equipment for performing the method according to the invention that includes in the tank, in its inlet zone, the basket for mechanical pre-treatment with a pre-connected inlet of purified sewage, the activation space with aerating elements, the feeding tank in which the feed roll connected by the feed adapter to the activation space is arranged, further on the recirculation sludge pump for pumping the activated sludge from the feeding tank bottom into the inlet zone and the purified sewage withdrawal consists in it that the feeding tank is equipped or connected to the source of intensive stirring of its content, that the feeding tank is connected to the pump for lowering the operating level whose outlet is mouthed in the withdrawal and that in the feeding tank the suction branch is arranged for sucking off the floating impurities from its lowered level, connected to the suction pump whose outlet is mouthed above the level of the inlet zone.
Advantageous is a design where the pump for lowering the operating level, the source of intensive stirring of the feeding tank content, the suction pump, and the recirculation sludge pump are designed as air-lift pumps.
A further feature is that the inlet zone in which the basket for mechanical pre-treatment is arranged is spacially delimited by the dipping wall.
Another feature is that in the inlet part of the purified sewage withdrawal mouthed into the outlet space the spillway is made delimiting the height of the operating level behind which the pump outlet for lowering the operating level is mouthed and at that the outlet space is delimited by a part of the feeding tank jacket equipped with passage, the slanting wall and the side walls.
For achieving a reliable performance of the purification process a design is advantageous according which the source of intensive stirring of the feeding tank content, the recirculation sludge pump, the pump for lowering the operating level, and the the suction pump are connected to the air distributor connected with the pressure air source and at that the air distributor and the pressure air source are controlled by a programmable control unit.